Three rocks, collected from the surface of the moon by a Soviet space mission in 1970, were sold for a whopping $855,000 at a New York auction on Thursday.

Sotheby’s auction house said the “moon rocks” are the only known documented lunar matter in private hands. They were offered for sale by an unidentified private American collector, who purchased them at auction in 1993 for $442,500.

Sotheby’s said that the buyer was an American, but did not disclose his/her name.